A couple of developments since the last time we discussed the syntax on this:
1. The CSSWG discussed the name of the 'bopomofo'/'right' value at the last
F2F, and someone suggested 'inter-character' as an alternative. (I suggest
correcting that to 'inter-base', since ruby bases can have more than one
character.)
2. In discussions around the similarly-functioning 'text-emphasis-position',
we came up with
text-emphasis-position: [above|below] && [left|right]
i.e. two keywords are specified in the value, one which takes effect in
horizontal typographic modes, the other of which takes effect in vertical
typographic modes.
We could use the same structure for 'ruby-position', which would give us
ruby-position: [ above | below | inter-base ] && [ left | right ]
e.g.
ruby-position: inter-base right; /* Traditional Chinese with bopomofo */
ruby-position: above right; /* PRC Chinese */
ruby-position: below right; /* Japanese */
We could even assume 'right' if the second half was dropped, since most
ruby is placed on the right in vertical text.
~fantasai